The NF-kappaB (NF-?B) family of dimeric transcription factors regulates diverse physiological processes including immune and inflammatory responses, cell proliferation and survival. The combinatorial NF-?B dimers are formed from five family members; p50, p52, RelA (p65), cRel and RelB. These dimers regulate transcription by binding to specific DNA sequences of target genes known as ?B sites. The long term goals of our laboratories are to understand how NF-?B dimers function specifically in gene regulation. To achieve that goal, we have pursued a variety of approaches ranging from the biophysical to the genetic. Recent studies have emphasized the role of post-translational modifications of NF-?B dimers and the role of dimer-specific co-activators in regulating specific target genes. The focus of this proposal is to examine transcriptional regulation by phosphorylation and coactivator recognition events. We employ genetic, genomic, biochemical and biophysical approaches to investigate the two NF-?B family members that play the most prominent roles in human disease: RelA and p52. In aim 1 experiments are designed to investigate the mechanisms of transcriptional control by the RelA:CBP/p300 complex. Several reports have demonstrated the importance of RelA phosphorylation, and CBP/p300 binding in target gene regulation. Other studies have revealed that the effect of this modification/interaction is not global. Each modification/interaction affects the expression of only a subset of genes in stimulus and cell type specific manner. In this study we will investigate the role of RelA phosphorylation and CBP/p300 interaction mechanism and its impact on gene regulation. In aim 2 Biophysical and in vivo experiments are designed to study the transcriptional control by the cancer-associated p52:Bcl3 complex. As homodimers, NF-?B p52 and p50 have been reported to associate with Bcl3 to activate transcription, and as such they play critical roles in immune organogenesis and tolerance. The goal of this aim is to investigate the molecular basis of how p52 homodimer associates with Bcl3 and the specificity of the interaction, and if these complexes target a subset of ?B sequences. Public Health Relevance: The NF-?B family of dimeric transcription activators, which regulates a large number of genes, is critical for maintaining normal cell physiology. The focus of this proposal is to understand the regulation of promoter and transcriptional coactivator recognition by the NF-?B dimers.